Meaning "firm, hard, compact" is from 1530s. Meaning "entirely of the same stuff" is from 1710. Of qualities, "well-established, considerable" c.1600. As a mere intensifier, 1830. Slang sense of "wonderful, remarkable" first attested 1920 among jazz musicians. As an adverb, "solidly, completely," 1650s. Solid South in U.S. political history is attested from 1858. Solid state as a term in physics is recorded from 1953; meaning "employing solid transistors (as opposed to vacuum tubes)" is from 1959. Related: Solidly.

n.

late 14c., "three-dimensional figure," from solid (adj.). Meaning "a solid substance" is from 1690s. Cf. also solidus; Latin solidus (adj.) was used as a noun meaning "an entire sum; a solid body."

Physics One of four main states of matter, in which the molecules vibrate about fixed positions and cannot migrate to other positions in the substance. Unlike a gas or liquid, a solid has a fixed shape, and unlike a gas, a solid has a fixed volume. In most solids (with exceptions such as glass), the molecules are arranged in crystal lattices of various sizes.